Slugging, and severe slugging, is a problem that is especially related to mature oil fields. As an oil well ages, gases and liquids in the multiphase hydrocarbons tend to separate in the flowlines and risers as the flowlines travel down an decline to a subsequent incline. Typically, this is due to the heavier liquids moving faster than corresponding gases, which results in the formation of liquid and gas pockets (i.e. slugs). The formation of slugs can result in large pressure and production fluctuations. Such pressure and production fluctuations can give rise to operational hazards and can damage equipment.
Present slug-mitigating measures include slowing down the rate of oil production or extraction, which can easily reduce oil production from normal levels by ten percent (10%). Reducing oil production to mitigate severe slugging not desirable.
Present slug-mitigating systems include certain mechanical means on the top-side, such as controllable chokes or valves with appropriate control algorithms. These techniques can be generally classified as “active” mitigation/control, as they regulate the amount of multiphase fluids flowing through the pipelines and risers in response to measured or sensed operating conditions (e.g., pressure, or flow rate).
Another class of slug-mitigating assemblies or systems is “passive” mitigation, in which the flow of multiphase hydrocarbons is not actively controlled with the system. The mitigation effect can be accomplished through a change in geometry of the piping system or flowline. For example, it is believed that the technology in U.S. patent application Ser. No. US2007/0028984, having a filing date of Feb. 8, 2007 and Colin G. Caro et al. as the named inventors, can mitigate slugging. The Colin et al. application discloses a spiral technology or small amplitude helical technology (SMAHT) that is produced by twisting a first pipe against a second pipe—similar to plaiting of ropes. In several examples, the first pipe has a larger diameter than the second pipe. SMAHT has an amplitude to pipe diameter ratio of less than or equal to 0.5, Moreover, the formation of SMAHT inherently deforms the cross-section of the first pipe, and possibly the second pipe, as the first pipe is bent and twisted around the second pipe.
Such slugging problems can also arise on land when piping multiphase hydrocarbons. Such slugging can occur at the intersection of a downwardly inclined portion of pipeline with an upwardly inclined portion of pipeline, such as through terrain having hills or mountains, which is known in the art as “terrain induced slugging.”